Whats a 6 lug d.b.factory application?

[Hawssie]

I know a lot of people change from 6 to 5 lug when they do disc brake conv. on 2wds. But since I am going to use steelie wheels I dont see the point for me to change. My question is what is an application I can use if I need to get the discs in six lug 2wd form? I see them sold at places like Early Classics etc. but what if you need them locally what year truck do I say I have to look up the right part, since the 1971-72s are 5 lug stock.